SAB 82532/SAF 82532
Character Oriented Serial Mode (MONOSYNC/BISYNC)
Semiconductor Group
79
07.96
7.4
Special Functions
7.4.1
If enabled via register CCR3, a programmable 8-bit pattern (register PRE) is transmitted
with a selectable number of repetitions after Interframe Timefill transmission is stopped
and a new frame is ready to be sent out.
Note: If the preamble pattern equals the SYN pattern, reception is triggered by the
preamble.
Preamble Transmission
7.4.2
If data transfer from system memory to the ESCC2 is done by DMA (DMA bit in XBCH
set), the number of characters to be transmitted is usually defined via the Transmit Byte
Count registers (XBCH, XBCL: bits XBC11 … XBC0).
Setting the ‘Transmit Continuously’ (XC) bit in XBCH, however, the byte count value is
ignored and the DMA interface of ESCC2 will continuously request for transmit data any
time 32 new characters can be entered in XFIFO.
This feature can be used to transmit frames of length higher than the byte count specified
by XBCH, XBCL (frames with more than 4095 bytes).
Note: If the XC bit is reset during continuous transmission, the transmit byte count
becomes valid again, and the ESCC2 will request the amount of DMA transfers
programmed via XBC11 … XBC0. Otherwise, the continuous transmission and
the generation of DMA input requests is stopped when a data underrun condition
occurs in XFIFO. Instead of CRC, continuous ‘1’s (IDLE) are transmitted
thereafter.
Continuous Transmission (DMA mode only)
7.4.3
If the internal CRC generator is not used for calculation of Frame Check Sequence, an
externally calculated checksum (16 bits) can be appended to the message frame without
internally generated parity information, although parity is enabled for data characters.
Prerequisites are:
CRC generator disabled (CAPP = ‘0’),
CON = ‘0’ for all data characters which are to be included into parity generation
(normal operation),
CON = ‘1’ for both bytes defining the CRC checksum,
Message End indication has to be issued after the checksum is written to XFIFO.
The programmed character length has no influence on this function.
CRC Parity Inhibit